1. Field of the Invention
The present invention relates to a laminate type ceramic electronic component and a method for manufacturing the laminate type ceramic electronic component, and more particularly, relates to a laminate type ceramic electronic component with an external electrode including a plating film formed directly by plating so as to be electrically connected to a plurality of internal electrodes, and a method for manufacturing the laminate type ceramic electronic component.
2. Description of the Related Art
As shown in FIG. 5, a laminate type ceramic electronic component 101 typified by a laminated ceramic capacitor generally includes a component main body 105 having a stacked structure, which includes a plurality of stacked ceramic layers 102 composed of, for example, a dielectric ceramic, and a plurality of layered internal electrodes 103 and 104 formed along the interfaces between the ceramic layers 102. The respective ends of the plurality of internal electrodes 103 and the respective ends of the plurality of internal electrodes 104 are exposed respectively at first and second end surfaces 106 and 107 of the component main body 105. Furthermore, external electrodes 108 and 109 are formed on first and second end surfaces 106 and 107 of the component main body 105 respectively so as to electrically connect the respective exposed ends of the internal electrodes 103 to each other and the respective exposed ends of the internal electrodes 104 to each other.
For the formation of the external electrodes 108 and 109, in general, a metal paste containing a metal component and a glass component is applied onto the edge surfaces 106 and 107 of the component main body 105, and then subjected to firing, thereby forming paste electrode layers 110 first. Next, first plating layers 111 containing, for example, Ni as their main constituent are formed on the paste electrode layers 110, and second plating layers 112 containing, for example, Sn or Au as their main constituent are further formed thereon. More specifically, each of the external electrodes 108 and 109 is composed of a three-layer structure of the paste electrode layer 110, the first plating layer 111, and the second plating layer 112.
The external electrodes 108 and 109 are required to have favorable solderability when the laminate type ceramic electronic component 101 is mounted onto a substrate with the use of solder. At the same time, the external electrode 108 is required to achieve the function of electrically connecting the plurality of internal electrodes 103 to each other, which are electrically insulated from each other, and the external electrode 109 is required to achieve the function of electrically connecting the plurality of internal electrodes 104 to each other, which are electrically insulated from each other. The second plating layers 112 described above serve to ensure the solderability, whereas the paste electrode layers 110 serve to electrically connect the internal electrodes 103 to each other and the internal electrodes 104 to each other. The first plating layers 111 serve to prevent solder erosion in solder joint.
However, the paste electrode layer 110 is large in thickness, from several tens μm to several hundreds μm. Therefore, in order to limit the dimensions of the laminate type ceramic electronic component 101 up to certain specifications, there is undesirably a need to reduce the effective volume for ensuring a capacitance because there is a need to ensure the paste electrode layers 110 in terms of volume. On the other hand, the plating layers 111 and 112 have a thickness on the order of several μm. Thus, if the external electrodes 108 and 109 can be composed of only the first plating layers 111 and second plating layers 112, the effective volume can be ensured so as to ensure the capacitance.
For example, Japanese Patent Application Laid-Open No. 63-169014 discloses a method for forming an external electrode, in which a conductive metal layer is deposited by electroless Ni plating on the entire sidewall surface of a component main body, at which internal electrodes are exposed, so as to short circuit the internal electrodes exposed at the sidewall surface.
However, the plating film formed directly by plating onto a surface of the component main body has a problem with the fixing strength between the plating film and the component main body, because glass such as in the case of the paste electrode layer described above is not interposed between the plating film and the component main body. In this case, as for the fixing strength, importance is placed on not only the fixing strength between the ceramic section in the component main body and the plating film but also the fixing strength between exposed ends of the internal electrodes and the plating film.
On the other hand, importance is also placed on the film strength (to be unlikely to be cracked) of the plating film. Moreover, it is relatively difficult to achieve a balance between the fixing strength and film strength of the plating film described above.
To explain more specifically, when the laminate type ceramic electronic component is mounted with soldering, a stress is applied to the external electrode. In this case, when the plating film is soft, the plating film is unlikely to be cracked, while the stress described above causes the plating film to peel off to cause a gap between the plating film and the component main body. Therefore, the ingress of moisture will be caused into the gap to degrade the insulation resistance, and thus possibly decrease the reliability of the laminate type ceramic electronic component. On the other hand, when the plating film is made harder, the fixing strength is improved, while the plating film is made fragile so as to be cracked, and thus the reliability of the laminate type ceramic electronic component decreases.